The present invention relates to a transmission line duplexing processing method, and apparatus, capable of transmitting data in layers higher than the TCP (Transmission Control Protocol) protocol by using a socket interface library and capable of easily operating in a workstation or the like, and relates to a recording medium for recording its processing procedure.
FIG. 1 shows an example of a configuration that signals can be sent and received between a plurality of personal computers via duplex transmission line (Ethernet). In FIG. 1, three personal computers PC1, PC2 and PC3 are interconnected via duplex transmission line, that is, an A transmission line (hereafter also referred to in some cases simply as A-line) BA and a B transmission line (hereafter also referred to in some cases simply as B-line) BB. Each the personal computers include software storage units S1, S2 and S3, device drivers D1, D2 and D3, and I/O units such as Ethernet card insertion units E1, E2, E3, E4, E5 and E6 for storing communication protocols.
FIG. 2 is a flowchart of data to be sent and received for explaining an example of a conventional transmission duplexing method. FIG. 2 shows the configuration of software corresponding to the hardware configuration of FIG. 1. In FIG. 2, there are shown applications 11 and 12 respectively stored in the software storage units S1 and S2 respectively of the personal computers P1 and PC2 shown in FIG. 1, duplexing processing units 21 and 22 respectively stored in the device drivers D1 and D2, TCP protocols 31 and 32 respectively stored in the Ethernet card insertion units E1 and E2, and E3 and E4, and Is protocols 41 and 42 stored in the Ethernet card insertion units E1 and E2, and E3 and E4.
The TCP protocols 31 and 32 are one method of establishing connections (both lines of the duplex transmission line) beforehand, and transmitting data by using the connections. In this case, the transmission data is not a block unit train, but a stream unit train.
Here, the xe2x80x9cblock unit trainxe2x80x9d means a cluster of transmission data in communication, and indicates data having a plurality of units each including, besides information data, transmission control characters. In the xe2x80x9cstream unit train,xe2x80x9d a large amount of data are handled simply as a bit train instead of clusters such as blocks or packets. Thus the xe2x80x9cstream unit trainxe2x80x9d means data formed of a plurality of byte units.
In the case the duplexing processing is performed by the duplexing processing units 21 and 22 in the above described configuration by using the TCP protocols 31 and 32, a connection is established through one of the transmission lines (such as BA). In the case where an abnormality has occurred on this transmission line BA, connection of the transmission line BB of the opposition line is established and the transmission is continued.
Even in the case where an abnormality is occurred on the transmission line BA, the TCP protocols 31 and 32 retries the sending. The user of the TCP protocols 31 and 32 cannot know up to which portion of the transmission data that the TCP protocols 31 and 32 are requested to send have been sent and which portion is being subjected to retry processing, because the TCP protocols 31 and 32 handle data (1), (2) and (3) of a stream unit train.
When one terminal device PC1 sends data toward the other terminal device PC2 in the order of (1), (2) and (3), the terminal device PC2 receives the data in the order of (1), (2) and (3), if the transmission line BA is normal.
However, if an abnormality has occurred on the transmission line BA during the transmission of, for example, (2), the transmission line is switched to the transmission line BB. Although the data is sent in the order of (1), (2) and (3), the terminal device PC2 cannot normally receive (2) among the received data. This results in received data lacking data, such as (1) and (3).
For transmitting data normally even in the case where an abnormality has occurred in one of the transmission lines, therefore, it is necessary to wait for the termination of the retry processing conducted by the TCP protocol, suspend the use of the one transmission line, then establish a connection using another transmission line, and perform transmission again. Since the retry time of the TCP protocol is typically in the range of 5 to 6 minutes, the switching to another transmission line cannot be effected. Over that time, therefore, the transmission is stopped.
An object of the present invention is to provide a transmission duplexing method and apparatus capable of continuing transmission without stopping even in the case where an abnormality has occurred on one of duplexed transmission lines, and a recording medium for recording its processing procedure.
A transmission line duplexing processing method according to the present invention comprises the steps of: installing duplex transmission line between a plurality of terminal devices, the duplex transmission line being duplicated by first and second transmission lines; making it possible to send and receive data of a stream unit train between the terminal devices by using a TCP protocol; sending the data of the stream unit train simultaneously to the transmission lines; receiving data, and handling only data which is included in the data sent at the sending step and which has arrived earlier, as received data; detecting an abnormality caused on either of the first and second transmission lines; and responding to detection of occurrence of the abnormality on the transmission line conducted at the abnormality detecting step, to close the transmission line having the abnormality and conduct sending and receiving by using a remaining normal transmission line.
Preferred manners for carrying out the present invention are as follows.
(1) The step of responding to detection of occurrence of an abnormality on a transmission line conducted at the abnormality detecting step, to store the data obtained immediately before the occurrence of the abnormality is further provided.
(2) The receiving step comprises the step of measuring receiving data size for each of the transmission lines when receiving data, deriving a difference between them, receiving only data of the difference, and receiving new data after disappearance of the difference.
(3) The abnormality detecting step comprises the step of measuring receiving data size for each of the transmission lines when sending data, deriving a difference between them, and judging the transmission line storing the difference to be abnormal when data of the difference has exceeded a prescribed value.
(4) The step of responding to detection of occurrence of an abnormality on a transmission line conducted at the abnormality detecting step and closing of the transmission line having the detected abnormality, to periodically request reestablishment of both of the transmission lines, and responding to restoration of the transmission line having the detected abnormality to a normal state and reestablishment of the closed transmission line, to conduct sending and receiving by using both of the transmission lines again is further provided.
With above configuration, the transmission can be continued without stopping even in the case where an abnormality has occurred in one of the duplexed transmission lines.
(5) The step of receiving head data when the closed transmission line has been reestablished, preventing the reestablished transmission line from being used until receiving data corresponding to the receiving size contained in receiving unit of a normal transmission line, and using reestablished both transmission lines only when an opposite line has received data corresponding to the receiving size contained in the header is further provided.
The order of the stream data is not disturbed, in addition to the above described advantage.
The present invention can be realized not only as a transmission line duplexing processing method, but also as an apparatus for realizing the method, or a computer-readable recording medium for recording its processing procedure.
As described above, according to the present invention, in a transmission line duplexing processing method, and apparatus, and a recording medium for recording the processing procedure, the transmission a can be continued without stopping, even in the case where an abnormality has occurred in one of the transmission lines.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.